mime_arg ?name msg creates a MIME-structured CGI argument
called name with contents msg. You can create msg by
either Netmime.memory_mime_message or
Netmime.file_mime_message.

work_around_backslash_bug : Whether to work around a bug
found in almost all browsers regarding the treatment of
backslashes. The browsers do not quote backslashes in file
names. This breaks RFC standards, however. This argument is
true by default.

name : set the name of the argument. If it is not given,
the name is extracted from the "Content-Disposition" field of
the msg header or it "" if this field is not found.

It is easy to manipulate lists of arguments with the List
module. For example, List.filter (fun a -> a#name <> n) args
will remove from args all occurrences of the argument with
name n. The following functions are helpers for operations
specific to arguments.